1. Chapter 4 Carbohydrate Metabolism

3. Glucose transport

4. Metabolism….. Time to put some LIFE into the subject What is Life? What are the properties of life? Movement Turnover of components Reproduction of one’s kind Energy Transformations Chemical Energy is the Dominant Energy Form in a Living System Chemical Energy is the Dominant Energy Form in a Living System

5. Metabolism: The process by which a living system derives or uses energy through chemical change AB Energy Anabolism: Synthesis. Putting free energy to work Catabolism: Degradation. Deriving free energy ATP: Energy currency. The standard that is used to gauge all energy compounds Endergonic Exergonic

6. Rule: Living system are able to conserve energy Rule: Heat is wasted energy Heat is energy that cannot be conserved Rule:Exergonic biochemical transformations channel a large part of the free energy into chemical bonds of the product. Rule: Catabolic reactions drive anabolic reactions Living systems will do their utmost to prevent lost of free energy as heat Rule: The 5 Rules of Energy Metabolism

7. Anaerobic Aerobic Reduced cofactors (drive Ox Phos) Reduced cofactors (drive Ox Phos) Oxidized cofactors (recycle back Oxidized cofactors (recycle back

8. The Glycolysis Pathway Major anaerobic pathway in all cells NAD + is the major oxidant Requires PO 4 Generates 2 ATP’s per glucose oxidized End product is lactate (mammals) or ethanol (yeast) Connects with Krebs cycle via pyruvate

9. Glycolysis  -D-Glucose Glucose-6-Phosphate Fructose-6-Phosphate CH 2 OPO 3 O CH 2 OH OH ATP Hexokinase Phosphogluco- isomerase O CH 2 OH OH O CH 2 OPO 3 OH

10. Fructose-6-Phosphate CH 2 OPO 3 O CH 2 OH OH CH 2 OPO 3 O OH Fructose 1,6-Bisphosphate ATP Phosphofructo- kinase-I CH 2 OPO 3 C=O CH 2 OH CHO H-C-OH CH 2 OPO 3 Dihydroxyacetone-PhosphateGlyceraldehyde-3- Phosphate Aldolase

11. CH 2 OP C=O HO-C-H H-C-OH C-OH CH 2 OP.. CH 2 OP C=O HO-C-H.. H-C-OH C-OH CH 2 OP + CHO ALDOLASE Dihydroxy Acetone Phosphate (DHAP) Glyceraldehyde-3-P H Fructose 1,6- bisphosphate

12. CH 2 OPO 3 C=O CH 2 OH CHO H-C-OH CH 2 OPO 3 Triose Stage Triose phosphate isomerase Dihydroxy acetone phosphate (DHAP) CHO H-C-OH CH 2 OPO 3 C H-C-OH CH 2 OPO 3 ~OPO 3 O PO 4 NAD + NADH + H++ H+ ADP ATP Glyceraldehyde-3-P Dehydrogenase COO H-C-OH CH 2 OPO 3 Glyceraldehyde 3-phosphate Phosphoglycerate Kinase Glycerate 1,3- bisphosphate Glycerate 3- phosphate

13. COO H-C-OH CH 2 OPO 3 COO C=O CH 3 COO H-C-OPO 3 CH 2 OH COO C~ CH 2 OPO3 Pyruvate 3-PGA 2-PGA PEP Phosphoglycero- mutase Enolase -H 2 O ADP ATP Pyruvate kinase L-lactate NADH + H + NAD + COO HO-C-H CH 3 Back to Glycolysis

14. Regulation of Glycolysis 6-phosphofructokinase-1 Allosteric enzyme negative allosteric effectors Citrate, ATP Positive allosteric effectors AMP, fructose1,6-bisphosphate, fructose2,6-bisphosphate Changes in energy state of the cell (ATP and AMP)

15. Regulation of Glycolysis fig.6-4

16. Regulation of Glycolysis Pyruvate Kinase Allosteric enzyme Inhibited by ATP. Isoenzyme in liver activated by fructose 1,6 bisphosphate inhibited by alanine Regulated by phosphorylation and dephosphorylation Hexokinase Different isoenzymes Hexokinase IV glucose 6-phosphate is an allosteric inhibitor promote biosynthesis

17. The Significance of Glycolysis Glycolysis is the emergency energy- yielding pathway Main way to produce ATP in some tissues red blood cells, retina, testis, skin, medulla of kidney In clinical practice

18. Aerobic Oxidation of Glucose Glucose oxidation 1. Oxidation of glucose to pyruvate in cytosol 2. Oxidation of pyruvate to acetylCoA in mitochondria 3. Tricarboxylic acid cycle and oxidative phosphorylation

19. Mechanism of pyruvate dehydrogenase complex Fig.6-6

20. O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 O2O2 METABOLISM OF PYRUVATE METABOLISM OF PYRUVATE Its time to get aerobic

21. COO C=O CH 3  ketoacid Carboxyl group (acid) Ketone group (carbonyl) Methyl group Pyruvate Structure – 2 -2 + 2 CH 3 C-OHC=O O –2 C O O Net = – 2 Oxidation of Carbon +2 Look for one NAD + for each glyceraldehyde-3-PO 4 oxidized to pyruvate -OH 0 0 H-C-OH CHO CH 2 OH P Glyceraldehyde 3-Phosphate

22. Decarboxylation Reactions Two Types: non-oxidative and oxidative No change in oxidation state of carbonyl C H 3 C-C:COO - O H 3 C-C+ O NAD + NADH H 3 C-C: O CO 2 Oxidized carbonyl C Oxidative Non-oxidative H 3 C-C:H O H+H+ H 3 C-C-OH O H2OH2O

23. The Energy Story of Glycolysis Overall ANAEROBIC (no O 2 ) Glucose + 2ADP + 2P i 2 Lactate + 2ATP + 2H 2 O Glucose + 2ADP + 2P i 2 Ethanol + 2CO 2 +2ATP + 2H 2 O Overall AEROBIC Yeast Glucose + 2ADP + 2P i + 2NAD + 2 Pyruvate + 2ATP + 2NADH + 2H + + 2H 2 O 5 ATPs

24. C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O CHO CH 2 OH H-C-OH OH-C-H H-C-OH D-Glucose  G o’ = -2,840 kJ/mol  G o’ = -146 kJ/mol C 6 H 12 O 6 2 C 3 H 4 O 3 Glucose2 Pyruvate COO - C=O CH 3 COO - C=O CH 3 5.2% Energy used 146 2,840 100 = Anaerobic Aerobic 2 Pyruvates

25. Glycolysis Oxidative phosphorylation pyruvate Krebs Cycle 3 NADH Glucose Galactose Fructose Mannose Fatty Acids 1 FADH 2 Lactate Amino Acids O2O2 H2OH2O Anaerobic Aerobic Acetyl-Coenzyme A Pyruvate dehydrogenase Complex Pyruvate dehydrogenase Dihydrolipoyl transacetylase Dihydrolipoyl dehydrogenase NAD Coenzyme A Lipoic acid Thiamin pyrophosphate FAD

26. Thiamin pyrophosphate CH 3 COOC O Pyruvate + Carbanion Vitamin B-1 : + CO 2

27. Pantothenate CH 3 C O Acetyl Group Thioester bond COENZYME A Acetyl-Coenzyme A B-vitamin HS-CH 2 -CH 2 -N H -P-O-P-O OO O O -C-C-C-CH 2 -O OH HOCH 3 H -C-CH 2 -CH 2 -N O Adenosine-3’- phosphate

28. Dihydrolipoate CHCH 2 SH HS COO 6,8 Dithiooctonoate (Reduced, gained 2 electrons) SS CH 2 CHCH 2 COO (Oxidized, lost 2 electrons) Long hydrocarbon chain Disulfide bond

29. E3E3 Pyruvate Dehydrogenase Complex FAD TPP S S E1E1 E2E2 Pyruvate Dehydrogenase Dihydrolipoyl Transacetylase Dihydrolipoyl dehydrogenase H H.. CH 3 -C OH S S C-CH 3 O.. H2H2 Acetyl-CoA HS-CoA NAD + NADH.. CH 3 -C O

30. Tricarboxylic Acid Cycle

31. All Mean the Same

32. Features Acetyl-CoA enters forming citrate Citrate is oxidized and decarboxylated 3 NADH, 1 FADH 2, and 1 GTP are formed Oxaloacetate returns to form citrate

33. Citrate 6 5 4 Isocitrate cis-Aconotate  -ketoglutarate Succinyl-CoA Succinate Fumarate Malate Oxaloacetate More ReducedMore Oxidized CO 2 Cycle Intermediates

34. CARBON BALANCE CH 3 C O ~ S-CoA Citrate Isocitrate  -ketoglutarate Succinyl-CoASuccinate Fumarate Malate Oxaloacetate CO 2 2 carbons in 2 carbons out 2 carbons in 2 carbons out 6 6 5 44 4 4 4

35. Reactions of Acetyl-CoA CH 3 -C~S-CoA O H.. Split here HS-CoA C-C~S-CoA H H O Carbanion COO C=O CH 2 COO OAA Acetylations or Acylations COO C-OH CH 2 COO Citroyl-CoA H2CH2C C=O S-CoA Citrate Synthase (a lyase) O-O- Citrate

36. CH 3 -C~SCoA O COO - C=O CH 2 COO - C-OH CH 2 COO - -CH 2 - - OOC HS-CoA CH 2 COO - HO-C-COO - CH 2 COO - Citric Acid or Citrate Acetyl-CoA Citrate Synthase Oxaloacetate (OAA)

37. CH 2 COO - HO-C-COO - H-C-COO - H CH 2 COO - C-COO - H CH 2 COO - H-C-COO - HO-C-COO - H -H 2 O+H 2 O Citrate cis-Aconitate Isocitrate Aconitase Isocitrate Formation

38. CH 2 COO - H-C-COO - HO-C-COO - H Isocitrate CO 2 NAD + NADH + H + COO - CH 2 C=O COO -  -Ketoglutarate Isocitrate Dehydrogenase

39. COO - CH 2 C=O COO -  -Ketoglutarate COO - CH 2 C~SCoA O Succinyl-CoA  -Ketoglutarate dehydrogenase Complex HS-CoA TPP Lipoic acid FAD NAD + CO 2

40. COO - CH 2 C~SCoA O COO - CH 2 COO - Succinate Succinyl-CoA GTPGDP PiPi + HS-CoA Succinyl-CoA Synthetase Thioester bond energy conserved as GTP

41. COOH C C C=O C COOH C C H H SuccinateFumarate FAD FADH 2 MalateOxaloacetate COOH C C OH H H2OH2O NAD + NADH + H +

42. ATP Generated in the Aerobic Oxidation of Glucose There are two ways for producing ATP Substrate level phosphorylation G1,3-BP to G-3-P, PEP to Pyruvate, SCoA to succinate Oxidative phosphorylation

43. ATP Generated in the Aerobic Oxidation of Glucose In aerobic oxidation of glucose 5 NAD+, 1 FAD Stoichiometry: 2.5 ATP per NADH 1.5 ATP per FADH Table 6-1

44. Pyruvate Dehydrogenase complex Pyruvate + TPP  Acetal-TPP + CO 2 Acetal-TPP + S-S  Ac-S ^ SH + TPP Ac-S ^ SH + HS-CoA  AcS-CoA + HS ^ SH HS ^ SH + FAD  S-S + FADH 2 FADH 2 + NAD +  FAD + NADH + H + Pyruvate + HS-CoA + NAD +  Acetyl-CoA + NADH + H + Regulators- Inhibitors Regulation of the Kreb’s Cycle Fatty acids and ATP Regulators-Activators and AMP

45. Key Regulatory Points: 1. Pyruvate dehydrogenase Complex Inhibited by NADH and Acetyl-CoA NADH [NAD + ] Acetyl-CoA HS-CoA High NADH means that the cell is experiencing a surplus of oxidative substrates and should not produce more. Carbon flow should be redirected towards synthesis. High Acetyl-CoA means that carbon flow into the Krebs cycle is abundant and should be shut down and rechanneled towards biosynthesis

46. Mechanism: NADH and acetyl-CoA reverse the pyruvate dehydrogenase reaction by competing with NAD + and HS-CoA 1. Competitive Inhibition 2. Covalent Modification (second level regulation) E-1 subunits of PDH complex is subject to phosphorylation Insulin Epinephrine Glucagon Cyclic-AMP protein kinase E 1 -OH E 1 -OPO 3 H2OH2O HPO 4 = ATP ADP PDH kinase PDH phosphatase Active Inactive TPP FAD 1 2 3 ATP

47. Regulation of the Citric Acid Cycle Primary modes: 1. Substrate availability (key enzymes are subsaturated) 2. Product inhibition 3. Feedback inhibition (competitive) Key regulators: 1. Acetyl-CoA (controls citrate synthase) 2. OAA (controls citrate synthase, regulated by NADH) 3. NADH (controls citrate synthase, isocitrate dehydrogenase 4.Calcium (stimulates NADH production) See Fig. 6-9 Allostery is not a primary mode

48. Pentose Phosphate Pathway

49. PENTOSE PHOSPHATE Pathway Glucose-6-PO 4  Ribose-5-PO 4 Synthesize NADPH for fatty acid synthesis Metabolize pentoses Take Home: The PENTOSE PHOSPHATE pathway is basically used for the synthesis of NADPH and D-ribose. It plays only a minor role (compared to GLYCOLYSIS) in degradation for ATP energy.

50. 1) NADPH (Nicotinamide Adenine Dinucleotide Phosphate, reduced form) is essentially identical in structure to NADH, with the exception of the phosphate at the 2’-position of the ribose ring of the adenine nucleotide. Just as NADH, the molecule consists of two nucleotides (heterocyclic, aromatic base attached to a ribose sugar at carbon-1 attached to a phosphate at carbon-5) attached to one another by a phosphoanhydride bond linking their 5’-phosphates. NADPH differs from NADH physiologically in that its primary use is in the synthesis of metabolic intermediates (NADPH provides the electrons to reduce them), while NADH is used to generate ATP by contributing its reducing power to the electron transport chain

51. Basic Process Found in cytosol Two phases Oxidative nonreversible Nonoxidative reversible

52. 2) The pentose phosphate pathway serves substantially two functions in cells: to provide ribose (a pentose) and its derivative 2-deoxyribose for nucleic acid synthesis (ribose is the sugar in RNA, 2-deoxyribose in DNA), and to provide NADPH as a reducing agent. The oxidation and decarboxylation of glucose-6-phosphate to ribulose-5- phosphate occurs in three steps, accompanied by the generation of two molecules of NADPH. The first step is the oxidation of the hydroxymethylene group at position one to a carbonyl group, yielding a lactone (cyclic ester) and a molecule of NADPH. The second step is then to hydrolyze the lactone to the free carboxylic acid. The carboxyl group of the carboxylic acid is then removed by oxidative decarboxylation, converting the 6-carbon sugar acid to a 5-carbon sugar, with the accompanying production of another molecule of NADPH.

53. 3) Once glucose-6-phosphate has been oxidized and decarboxylated to ribulose-5-phosphate, this latter keto-sugar is converted to the corresponding aldose, ribose-5-phosphate, by the enzyme phosphopentose isomerase. The ribose-5-phosphate produced in this way can now be used in the synthesis of nucleotides for incorporation into nucleic acids. The reaction proceeds through an enediol (C=C double bond and two hydroxyl groups) intermediate, as the enzyme takes advantage of the dissociability of the hydrogen on the terminal hydroxyl group to generate an oxyanion and move the C=O double bond to the terminal carbon, producing the aldehyde and reducing the ketone to an alcohol.

54. 4) In order to control ribose synthesis, a mechanism exists to remove this sugar when it is in excess, by converting it to glycolytic intermediates. A series of three enzymatic steps are carried out, transferring two- and three-carbon fragments from one sugar to another, and all of these steps are similar in mechanism to an aldol condensation (remember that aldolase, the enzyme in glycolysis which fragments the six-carbon, bisphosphorylated sugar fructose- 1,6-bisphosphate to two phosphorylated three-carbon fragments, breaks the carbon-carbon bond through the reverse mechanism of the aldol condensation). In these cases, however, the enzyme functions by cleaving a fragment from the donor sugar by a reverse aldol condensation, and then attaches it to the acceptor sugar using the forward reaction. The enzymes are transketolase, which transfers a two-carbon fragment terminating on the interior side in a carbonyl, and transaldolase, which transfers a three-carbon fragment terminating on the interior side in a hydroxymethylene group.

55. 5) The first reaction which assists in the conversion of ribose-5- phosphate to glycolytic intermediates, catalyzed by transketolase, is the transfer of the 1- and 2-carbons from xylulose-5-phosphate to the 1-carbon of ribose-5-phosphate. This leaves the last three carbons from xylulose-5-phosphate as glyceraldehyde-3-phosphate, the first three-carbon fragment encountered in glycolysis, and sedoheptulose- 7-phosphate, formed from the ribose-5-phosphate, which is a seven- carbon sugar.

56. 6) Xylulose-5-phosphate is an unusual sugar which is produced from ribulose-5-phosphate, simply by inverting the configuration at carbon-3. This reaction is carried out by the enzyme phosphopentose epimerase, and is freely reversible. Thus, in the first reaction converting ribose-5-phosphate to glycolytic intermediates, both ribose-5-phosphate and ribulose- 5-phosphate (the latter in the form of xylulose-5-phosphate) are being degraded to other species, and ultimately carried off in glycolysis.

57. 7) The second reaction which leads from intermediates in the pentose phosphate pathway to glycolytic intermediates is mediated by transaldolase. This enzyme transfers a three-carbon fragment (carbons 1, 2 and 3) from the sedoheptulose-7-phosphate just formed in the first reaction to the glyceraldehyde-3-phosphate just formed in the first reaction, yielding a four-carbon fragment, erythrose-4- phosphate, and a six-carbon fragment, fructose-6-phosphate. The fructose-6-phosphate is now free to enter the glycolytic pathway.

58. 8) The final reaction leading from intermediates in the pentose phosphate pathway to glycolytic intermediates is carried out by transketolase, just as was the first reaction. In this reaction, another molecule of xylulose-5-phosphate is cleaved, and the two-carbon fragment consisting of carbons 1 and 2 is transferred to the molecule of erythrose-4-phosphate just formed in the transaldolase reaction, yielding a molecule of glyceraldehyde-3-phosphate and another molecule of fructose-6-phosphate. Both of these products are capable of entering glycolysis directly, and so there are no leftover fragments produced in this overall conversion. Because another molecule of xylulose-5-phosphate has entered the reaction, the overall conversion consists of two molecules of xylulose-5-phosphate and one molecule of ribose-5-phosphate going to two molecules of fructose-6-phosphate and one molecule of glyceraldehyde-3- phosphate; the xylulose-5-phosphate can be produced from ribose-5-phosphate through ribulose-5-phosphate, and so the net reaction is the removal to glycolysis of three molecules of ribose-5-phosphate.

59. 9) Because the NADPH and ribose-5-phosphate produced by the pentose phosphate pathway are used for quite different purposes, it is sometimes necessary to produce them in different amounts. Therefore, the cell has different modes in which the pentose phosphate pathway can function. In the case where much more ribose-5-phosphate is required than NADPH, the ribose-5-phosphate is produced from glyceraldehyde-3-phosphate and fructose-6-phosphate by running the transaldolase and -ketolase reactions in reverse. This allows the cell’s NADP + supply to remain essentially unaffected

60. 10) When both NADPH and ribose-5-phosphate are needed in large amounts, the predominant reaction used by the cell to generate them is the conversion of glucose-6-phosphate to ribose-5-phosphate, with the liberation of two molecules of NADPH for each molecule of glucose-6-phosphate converted.

61. 11) When much larger amounts of NADPH are required than ribose- 5-phosphate, the conversion of glucose-6-phosphate to ribose-5- phosphate is the main reaction used, but the ribose-5-phosphate is immediately recycled through the transaldolase and -ketolase reactions, with gluconeogenesis returning the fructose-6-phosphate and glyceraldehyde-3-phosphate to glucose-6-phosphate for another round.

62. 12) An alternative use of the pentose phosphate pathway can be implemented when NADPH is needed in great quantity while ribose-5-phosphate is not. This use involves not recycling the ribose-5-phosphate to glucose-6-phosphate, but rather carrying the glycolytic intermediates forward, rather than backward. The final destination of the ribose-5-phosphate in this case is thus pyruvate, which can enter the Citric Acid Cycle as acetyl CoA and produce ATP. This mode is implemented when the cell requires both NADPH and ATP or NADH, rather than predominantly NADPH.

63. 13) An important use of the NADPH produced in the pentose phosphate pathway is in the maintenance of a reducing environment in the cell. In order to reduce oxidized sulfhydryls back to their free states in the laboratory, we use mercaptoethanol or dithiothreitol, but the cellular equivalent of this reducing agent is glutathione. Glutathione is a tripeptide, similar in structure to Glu-Cys-Gly, but with the exception that the glutamate residue is ligated to the cysteine through the R-group carboxyl, rather than the normal peptide-forming carboxyl (attached to the  -carbon). The sulfhydryl group of the cysteine R-group functions as the reducing agent, and recombines with disulfide bonds in a variety of molecules to release as a free sulfhydryl one of those partners in the disulfide. Another molecule of glutathione carries out the same reaction on the glutathione-subject molecule disulfide, releasing the other partner and producing an oxidized glutathione dimer. NADPH is used to reduce both glutathiones back to the sulfhydryl form, such that they can carry out this reaction again. In this way, the cell protects its components from the activities of reducing agents, as free sulfhydryls perform a variety of needed functions in cellular molecules.

64. Glycogen Formation and Degradation 93% of glucose units are joined by a-1,4- glucosidic bond 7% of glucosyl residues are joined by a- 1,6-glucosidic bonds Fig.6-11

65. Glycogen Formation and Degradation Main Chain: branch point every 3 units Branch: 5-12 glucosyl residues High Solubility many terminals 4 hydroxyl groups More reactive points for synthesis and degradation.

66. GLYCOGEN SYNTHESIS ENZYMES UDP-glucose pyrophosphorylase forms UDP-glucose Glycogen Synthase major polymerizing enzyme a1.,4->1,6-glucantransferase UDP-glucose pyrophosphorylase forms UDP-glucose Glycogen Synthase major polymerizing enzyme a1.,4->1,6-glucantransferase

67. Glycogen Synthesis Glycogen Glucose-1-PO 4 UDP-GlucoseGlucose-6-PO 4 Degradation Synthesis

68. GLYCOGEN SYNTHESIS ACTIVATION OF D-GLUCOSE GLYCOSYL TRANSFER BRANCHING ACTIVATION OF D-GLUCOSE GLYCOSYL TRANSFER BRANCHING

69. ACTIVATION UDP-GLUCOSE G-1-P + UTP UDP-GLUCOSE + PPi 2 Pi UDP-Glucose pyrophosphorylase

70. Glucose 1-PO 4 UDP-Glucose Glycogen Glycogen Synthase Phosphorylase UDP-glucose pyrophosphorylase Glucose 1-PO 4 + UTP UDP-Glucose + PP i  G o’ (kJ mol -1 ) H 2 O + PP i 2 P i Glucose 1-PO 4 + UTP + H 2 O UDP-Glucose + 2 P i ~0 -33.5 The hydrolysis of pyrophosphate drives this reaction Activated glucose UTP PP i

71. GLYCOSYL TRANSFER NON-REDUCING END UDP NEW

72. BRANCHING Glycogenin Cleave a1.,4->1,6-glucantransferase

73. Glycogen Degradation (Glycogenolysis) Glycogenolysis is not the reverse of glycogenesis

74. Glycogen Breakdown Glycogen Glucose-1-Phosphate Glucose-6-Phosphate Phosphorylase and Debranching Enzyme PO 4 Glucose Glycolysis Phosphoglucomutase Take home: Glycogen contributes glucose to glycolysis and to blood glucose (Liver)

75. O O O CH 2 OH HO-P-OH O O O O CH 2 OH HOHO PHOSPHORYLYSIS Glucose-1-PO 4 Phosphorylase HO-P-OH O O O O O CH 2 OH HO O-P-OH O O O CH 2 OH HO

76. Glycogen Phosphorylase N C N C Glycogen Storage Site Can accommodate on 4-5 sugars Pyridoxal 5’-PO 4 at active sites

77. Cyclic AMP PHOS B Phosphorylase: A Homo Dimer PHOS A 2 ATP 2 ADP Phosphorylase B Kinase * More active 2 H 2 O 2 PO 4 Less Active Covalent Phosphorylase Phosphatase PHOS B More active + 2 AMP - 2 AMP Allosteric + Immediate Hormonal Regulation

78. Debranching Enzyme  1,4  1,4 glucantransferase  1,6-gluglucosidase D-glucose Limit Branch Glycogen + Phosphorylase Highly branched core

79. TAKE HOME: What activates glycogen degradation inactivates glycogen synthesis. What activates glycogen synthesis inactivates glycogen degradation DEGRADATION SYNTHESIS RECIPROCAL REGULATION

80. Glycogen Glucose-1-PO 4 UDP-GlucoseGlucose-6-PO 4 Phosphorylase a Phosphorylase b PO 4 Glycogen synthase a Glycogen synthase b PO 4 ATP ADP PO 4 H2OH2OH2OH2O ATP ADP Active Less Active Active

81. The Significance of Glycogenesis and Glycogenolysis Liver maintain blood glucose concentration Skeletal muscle fuel reserve for synthesis of ATP

82. Glycogen Storage Diseases Deficiency of glucose 6-phosphatase liver phosphorylase liver phosphorylase kinase branching enzyme debranching enzyme muscle phosphorylase Table 6-2

83. Gluconeogenesis The process of transformation of non- carbohydrates to glucose or glycogen Principal organs liver, kidney Non-carbohydrates glucogenic amino acids lactate glycerol organic acids

84. Blood Glucose Blood Glucose Ribose 5-PO 4 Glycogen L-lactate Pyruvate PEP 2PGA 3PGA 1,3 bisPGA Gly-3-P F1,6bisP OAA F6P G6P DHAP Glucose H2OH2O PO 4 Phosphatase H2OH2OPO 4 Phosphatase Kinase

85. Gluconeogenesis Synthesis of glucose de novo (from scratch) An anabolic pathway for the synthesis of glucose from L-lactate or smaller precursors. Significance: Primarily in the liver (80%); kidney (20%) Maintains blood glucose levels The anabolic arm of the Cori cycle

86. L-lactate Pyruvate PEP 2PGA 3PGA 1,3BPGA L-alanine Gly3PDHAP Stage I Gluconeogenesis F1,6BP OAAL-malate OAA Mitochondria Glycerol L-aspartate PEP carboxykinase PEPCK Pyruvate Carboxylase Pyruvate Carboxylase 1 2

87. Pentose Phosphate F1,6BP F6P G6PG1PUDP-glucose Glycogen Glucose R5P Fructose 1,6 - bisphosphatase PFK-1 Glucose-6-phosphatase Stage II Gluconeogenesis Hexokinase 3 4

88. Problems: 3 irreversible reactions  G o’ = - 61.9 kJ per mol PEP Pyruvate F-1,6 bisPO 4 F-6-PO 4  G o’ = - 17.2 kJ per mol Glucose-6-PO 4 Glucose  G o’ = - 20.9 kJ per mol Take home: Gluconeogenesis feature enzymes that bypass 3 irreversible KINASE steps Take home: Gluconeogenesis feature enzymes that bypass 3 irreversible KINASE steps

89. Second Entry Point for Pyruvate CO 2 Fixation ReactionsSwinging Arm Biotin’s only function is to fix CO 2 Pyruvate carboxylase

90. Biocytin O O S NN C- O CH 2 C=0 Carboxy Biotin Carboxy group HN CH 2 C Carboxylase Enzyme Swinging Arm (the cofactor of biotin) Attach to Enzyme at lysine  -amine group Attach to Enzyme at lysine  -amine group

91. 3 Bypasses in Gluconeogenesis PEP Fructose 1,6bisPO 4 Glucose-6-PO 4 Glucose Fructose-6-PO 4 OAA GTP GDP CO 2 COO C=O CH 2 COO C~O CH 2 PO 3 PEP Carboxykinase PO 4 Fructose 1,6 bisphosphatase Glucose 6 phosphatase H2OH2O H2OH2O

92. THE CORI CYCLE Liver is a major anabolic organ Muscle is a major catabolic tissue L-lactateD-glucose L-lactate Blood Glucose Blood Lactate

93. Cori Cycle

94. REGULATION Rule 2. Kinases in glycolysis; phosphatases in synthesis Exception: PEPCK in synthesis - cAMP Rule 1. Allosteric are targets of metabolite regulators (effectors) Rule 3. ATP, citrate, acetyl-CoA, G6P turn on synthesis ENZYMES POSTIVE EFFECTORS FOCUS ON CARBON FLOW L-lactate Glucose (Synthesis) Glucose Pyruvate(Degradation) AMP, F2,6BP,turn on degradation NEGATIVE EFFECTORS Rule 4. ATP, acetyl-CoA, citrate,G6P turn off degradation AMP, F2,6BP turn off synthesis (Allosteric, cAMP-dependent, organ-specific isozymes) RECIPROCAL REGULATION

95. The Significance of Gluconeogenesis Replenishment of glucose and maintaining normal blood sugar level Replenishment of liver glycogen “three carbon” compounds Regulation of Acid-Base Balance Clearing the products lactate, glycerol Glucogenic amino acids to glucose

96. Blood Sugar and Its Regulation Blood sugar level 3.89-6.11mmol/l Major source of blood glucose digestion and absorption of glucose from intestine Glycogenolysis and gluconeogenesis Fig.6-18

97. Regulation of Blood Glucose Concentration Insulin decreasing blood sugar levels Glucagon, epinephrine glucocorticoid increasing blood sugar levels